Drive device for a windscreen wiper

ABSTRACT

In a drive mechanism for a windshield wiper, a switch disk for realizing a park position switch is supported so as to be independently rotatable relative to an output gear of a gear unit. The output gear and the switch disk are coupled with each other via a coupling device, with the coupling device acting as an engaging device carrying the switch disk along, in one direction of rotation only. In order to lower an axial dimension of the gear unit, the disk is rotatably supported on a sleeve, through which an output shaft extends so that the end of the shaft can support itself directly on a housing lid.

TECHNICAL FIELD

This invention relates to a drive mechanism for a windshield wiper.

BACKGROUND OF THE INVENTION

Drive mechanisms for windshield wipers are provided with switches takingcare of further supplying current to the motor of the drive mechanism,after the main switch has been opened by the driver, until thewindshield wiper will again have reached its home position also referredto as park position. Correspondingly, the name of this switch is parkposition switch.

Usually, the park position switches are realised by a switch disk havinga plurality of concentric contact paths which are sectionallyinterrupted and where, in each of the paths, a point-contact element issliding, establishing an electrically conductive contact towards thecontact path. Often, these contact paths are arranged fast on the outputgear of the output shaft while the point contacts are formed on contactsprings which are formed fast with the housing.

In this arrangement, where one element of the park position switch isconnected fast with the output shaft, there are some problems.

Outside influences, such as snow on the windshield, may prevent thewindshield wiper blade from reaching its park position. As, however, theoutput shaft will continue to be driven by the motor until it will haveadopted an angular position which corresponds to the park position ofthe wiper blade, with the movement being unhindered, the wiper arm andwiper blade will be bent elastically as they support themselves on theobstacle. As soon as the motor automatically turns off, the relaxingwiper will cause the output shaft to be rotated back. In consequence,the park position switch will be closed again and current will besupplied to the motor. As a result, the wiper will again be movedagainst the obstacle and there will again be forming a mechanic stress.This operation will repeat itself until the obstacle has been removed.It is easy to see that, in this action, the gear unit is acted upon byconsiderable stresses reducing its service life.

Therefore, DE 36 06 891 A1 already suggested to connect one part of thepark position switch to the output shaft via a coupling element insteadof connecting it fast with the output shaft. In the Published PatentApplication mentioned, the contact paths are arranged fast in thehousing and the point-contact elements are rotatably supported andconnected with the output shaft via a coupling device. However, thisprinciple is also applicable if the point-contact elements are formedfast with the housing and the contact paths are formed on a switch diskrotatably supported in the housing. In this case, the switch disk isconnected with the output shaft via a coupling element.

The coupling is of such a design that, in normal operation, when thewiper is driven to perform a pendulum movement, the output shaft willcarry along the switch disk so that the park position switch works likea park position switch which is connected fast with the output shaft.

However, if there comes up the above-discussed case where the outputshaft is reset, contrary to its actual direction of rotation, the switchdisk will not be carried along so that the park position switch, whichotherwise, again, would supply current to the motor, will not be closed.

In the Published Patent Application mentioned, the switch devicefeatures a design where the rotatable element is rotatably supported ona pivot connected with the housing lid, with the output shaft beingaxially supported on the front face of the pivot. The disadvantage ofthis arrangement is that, as compared with a conventional design, theaxial extension of the gear housing is increased by at least the heightof the housing pivot.

Therefore, in order lower an axial dimension of the housing, thisinvention suggests to support the rotatably supported switch element ona supporting sleeve formed on the housing lid and to have the outputshaft extend into the sleeve.

This arrangement, moreover, is beneficial in that the output shaft cansupport itself on the housing lid directly. Belonging to the outputshaft is also that part of the output gear which extends like a cap overthe front face of the output shaft.

The housing lid consists of a base plate of metal, with the supportingsleeve being of plastic injection-moulded onto the metallic base plate.The part of the base plate whereon the output shaft is supported is keptfree of plastic so that the axial forces will directly be introducedinto the base plate which is directly fastened on the edge of the gearhousing.

Provided on the outside of the base plate is a plastic layer whereinconductive tracks are extending via which the point contacts of the parkposition switch as well as the connected electric motor are suppliedwith current, and it is an obvious development to design the supportingsleeve and this plastic layer in one piece.

The rotatable switch element consists of an annular disk of plastic theinside edge of which rests on the outside surface of the supportingsleeve. Either the outside of the supporting sleeve or the insidecontour of the annular disk may feature a polygonal design so that thesupporting sleeve and the annular disk will touch each other only atcertain points. Lubricant may be deposited in the clearances betweenthese certain points of contact. The concentric contact paths are formedon the side of the annular disk which faces the lid.

The contact points are formed on contact springs approximatelydistributed evenly over the circumference of the contact disk so thatthe pressure applied by the contact springs to the annular disk willcause no tilting moment.

The contact springs are fastened to the bottom side of the plasticlayer. To this end, the metallic base plate features appropriate oblongapertures whereby sections of the plastic layer are bared downwards. Thecontact springs are fastened to these bare spots and connected with theconductive tracks in the plastic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section through the gear unit.

FIG. 2 is a top view on the metallic base plate of the gear housing lid.

At first, reference will be made to FIG. 1.

FIG. 1 shows a cup-shaped housing 1 the open side of which is closed bya lid 2. An output shaft 3 extends through the bottom of the housing 1.Fastened to the end of the output shaft 3, which extends into thehousing 1 is a gear 4 of plastic. The gear 4 has a cap-like portion 5,which extends across the front face of the shaft 3, which extends intothe housing. The radial extension of the gear 4 approximatelycorresponds to the inside diameter of the housing 1. The outsidetoothing 6 of the gear is in mesh with a worm not represented here andformed in direct prolongation of the armature shaft of the motor 7likewise not represented.

The lid 2 consists of a base plate 10 and of a plastic layer 11essentially extending on the outside of the base plate 10. Arranged inthis plastic layer are flat conductive tracks 12, which are connectedwith a plug 13, on the one hand, and with contact springs 14, on theother hand, out of, which one spring is represented in FIG. 1. On theirends, the contact springs 14 carry a point contact 15 cooperating withthe contact paths on the contact disk 20. The plastic layer 11 isfollowed by a supporting sleeve 16 extending axially into the inside ofthe gear housing 1. The connection between the plastic layer and thesupporting sleeve 16 is made through a plurality of apertures 17 in thebase plate 10, which are evenly distributed over a circle incorrespondence with the diameter of the supporting sleeve 16.

The end of the supporting sleeve 16 which faces the lid, is confined bythe base plate 10.

The end of the shaft 3 projects into the space formed by the sleeve andthe base plate 10 and is covered by a cap-like portion of the gear 4.The front side of this cap features an elevation supported on the baseplate 10. In this way, the axial forces acting on the shaft 3 areintroduced directly into the base plate 10 which, in its edge area, isdirectly connected with the housing 1 by means of screws or rivets 18.

The switch disk 20 is formed by an annular disk slipped onto the outsideof the supporting sleeve 16, with the inside diameter of the annulardisk essentially corresponding to the outside diameter of the supportingsleeve 16. Fixed on the surface of the annular disk 20, which faces thelid, are conductive contact paths 21. An annular collar 22 is formed onthe annular disk. This annular collar 22 is rested against the baseplate and thus forms an axial stop for the annular disk.

The annular disk 20 is fixed on the supporting sleeve 16 by means of aclamping ring 23, while a resiliently elastic corrugated ring 24 and acollar are arranged between the clamping ring 23 and the switch disk 20.

The inside edge of the switch disk 20 has the contour of a polygon, withthe flat connecting sides between the comers lying tangentially againstthe cylindrical outside surface of the sleeve. The clearances formed inthe comers serve to receive lubricant.

In order to couple the gear 6 and the switch disk 20, both the gear 4and the switch disk 20 are each provided with an elevation 25, 26 whichboth extend axially and rest with one side surface each against eachother, with the elevation 26 of the switch disk being able to move in adirection of rotation, away from the elevation 25 of the gear 4.

FIG. 2 shows the base plate 10 of the lid 2. On its outside edge, thebase plate 10 is provided with a plurality of apertures 30 serving asholes for screws or rivets for connecting the base plate 10 with theedge of the housing 1. Discernible in the centre of the base plate 10 isa circle of six apertures 17, which, as already explained, serve toallow the plastic mass which forms the supporting sleeve 16, to passthrough during the process of injection moulding, so that a closeconnection will be formed between the sleeve and the plastic layer.

Slots 31 extending along the tangential direction are provided aroundthe centre. In the area of the slots, the plastic layer is bare so as topermit the tongues 14 to be fastened there, on the free ends of thesecontact springs the contact points 15 being arranged, whilesimultaneously an electrically conductive contact is established towardsthe conductive tracks in the plastic layer.

What is claimed is:
 1. A drive mechanism for a windshield wiper,comprising: a drive shaft and a driving gear, which are arranged in ahousing closed by a lid, a drive-shaft-actuatable switch device for apark position switch, which is provided with rotatably supported firstcontacts movable by means of the drive shaft in such a way that thefirst contacts are carried along upon a rotation of the drive shaft inone direction and the first contacts are not carried alone when thedrive shaft rotates in another direction, and with second contactsarranged fixedly with the housing, wherein the housing lid includes asupporting sleeve for supporting the rotatably supported first contactsand wherein the drive shaft extends into the supporting sleeve.
 2. Adrive mechanism as claimed in claim 1, wherein the lid is provided witha metallic base plate, and the drive shaft supports itself on the baseplate.
 3. A drive mechanism as claimed in claim 2, further including aplastic layer provided on the outside of the base plate, electricallyconductive metal tracks being arranged in the plastic layer.
 4. A drivemechanism as claimed in claim 3, wherein the supporting sleeve and theplastic layer are made in one piece.
 5. A drive mechanism as claimed inclaim 1, wherein the first contacts are arranged on a disk slipped ontothe supporting sleeve and in that the rotatable contacts are made ascontact paths on the disk.
 6. A drive mechanism as claimed in claim 5,wherein outside of the supporting sleeve or the inside contour of thedisk is made as a polygon so that the supporting sleeve and the disktouch each other only at points, clearances between the points servingto receive lubricant.
 7. A drive mechanism as claimed in claim 1,wherein the base plate is provided with apertures, and on the bottomside of the plastic layer, which projects respectively across or intothe apertures, contact springs are arranged connected with theconductive tracks in the plastic layer in an electrically conductivemanner.